DiscreteAngle.java

// Copyright 2003, SLAC, Stanford, U.S.A.
package org.freehep.util;

import java.util.Iterator;
import java.util.SortedSet;
import java.util.TreeSet;

import org.geogebra.common.util.debug.Log;

/**
 * Calculates a discrete angle from an arbitrary angle, based on a set of given
 * angles.
 *
 * The class calculates the angle by dividing 360 degrees into segments based on
 * the discrete angles. It then will calculate the closest discrete angle for a
 * given angle. Discrete angles can be added and removed.
 *
 * This class can be used to constrain the mouse movement (or its result) if one
 * wants to draw under certain angles only.
 *
 * @author Mark Donszelmann
 * @version $Id: DiscreteAngle.java,v 1.5 2008-10-23 19:04:04 hohenwarter Exp $
 */
public class DiscreteAngle {

	private SortedSet angles;

	public DiscreteAngle() {
		angles = new TreeSet();
	}

	/**
	 * Returns the closest angle to any discrete angle in the set. Returns
	 * itself if the set is empty. Returns the only discrete angle if the set
	 * only contains one angle.
	 */
	public double getAngle(double angle) {
		if (angles.isEmpty()) {
			return angle;
		}

		Iterator i = angles.iterator();
		Double prev = (Double) i.next();
		if (!i.hasNext()) {
			return prev.doubleValue();
		}

		while (i.hasNext()) {
			Double cur = (Double) i.next();
			double cutoff = (cur.doubleValue() - prev.doubleValue()) / 2.0
					+ prev.doubleValue();
			if (angle <= cutoff) {
				return prev.doubleValue();
			}
			prev = cur;
		}
		return prev.doubleValue();
	}

	/**
	 * Adds a discrete angle to the set.
	 */
	public Double addAngle(double angle) {
		Double a = new Double(angle);
		angles.add(a);
		return a;
	}

	/**
	 * Removes a discrete angle from the set.
	 */
	public boolean removeAngle(double angle) {
		for (Iterator i = angles.iterator(); i.hasNext();) {
			Double r = (Double) i.next();
			if (r.doubleValue() == angle) {
				return removeAngle(r);
			}
		}
		return false;
	}

	/**
	 * Removes a discrete angle from the set.
	 */
	public boolean removeAngle(Double angle) {
		return (angle != null) ? angles.remove(angle) : false;
	}

	@Override
	public String toString() {
		StringBuffer s = new StringBuffer();
		s.append("Angles: ");
		for (Iterator i = angles.iterator(); i.hasNext();) {
			Double r = (Double) i.next();
			s.append(r.doubleValue());
			if (i.hasNext()) {
				s.append(", ");
			}
		}
		return s.toString();
	}

	public static void main(String[] args) {
		DiscreteAngle da = new DiscreteAngle();
		da.addAngle(0);
		da.addAngle(90);
		da.addAngle(180);
		da.addAngle(270);
		da.addAngle(360);

		da.addAngle(10);
		da.addAngle(190);

		Log.debug("  0 results in " + da.getAngle(0));
		Log.debug("  1 results in " + da.getAngle(1));
		Log.debug("  5 results in " + da.getAngle(5));
		Log.debug(" 80 results in " + da.getAngle(80));
		Log.debug(" 90 results in " + da.getAngle(90));
		Log.debug("170 results in " + da.getAngle(170));
		Log.debug("185 results in " + da.getAngle(185));
		Log.debug("186 results in " + da.getAngle(186));
		Log.debug("231 results in " + da.getAngle(231));
		Log.debug("359 results in " + da.getAngle(359));

	}
}